Nitride semiconductor laser device and semiconductor laser apparatus

ABSTRACT

A nitride semiconductor laser device at least includes a ridge part disposed on a second-conductivity-type semiconductor layer, a conductive oxide layer covering the upper surface of the ridge part and portions of opposite side surfaces of the ridge part, a dielectric layer covering a portion of the conductive oxide layer, and a first metal layer covering the conductive oxide layer and the dielectric layer, wherein a portion of the conductive oxide layer disposed on the upper surface of the ridge part is exposed through the dielectric layer and covered with the first metal layer.

BACKGROUND 1. Field

The present disclosure relates to a nitride semiconductor laser deviceincluding, as an electrode material, conductive oxide, and asemiconductor laser apparatus including the nitride semiconductor laserdevice.

2. Description of the Related Art

Conductive oxide exhibits lower visible light absorbance than metallicelectrodes formed of, for example, gold, and has lower refractive indexthan nitride semiconductors. Thus, it has been proposed that conductiveoxide is used to form a layer having both of a function of a conductiveelectrode and a function of cladding for a laser beam in a nitridesemiconductor laser device having a ridge shape.

As such a semiconductor laser device of this type, for example, JapaneseUnexamined Patent Application Publication No. 2006-41491 discloses thata blocking layer having a strip opening is disposed on a multilayeredbody of semiconductor layers, and a conductive oxide layer is formed onthe blocking layer to dispose a cladding layer electrode having aridge-shaped protrusion.

In addition, for example, Japanese Patent No. 5742325 discloses asemiconductor laser device in which a rid e is formed on the uppersurface of a p-type nitride semiconductor layer, a conductive oxidelayer is formed on the upper surface of the ridge, and a dielectriclayer is formed over all the side surfaces of the ridge.

In such an existing configuration, referring to FIG. 11 illustrating asemiconductor laser device 90 as an example, a p-type nitridesemiconductor layer 91 is formed so as to have a ridge shape(protrusion). A conductive transparent electrode 92 is formed on theupper surface of the p-type nitride semiconductor layer 91, and adielectric film 93 is formed from the upper surface to the side surfacesof the p-type nitride semiconductor layer 91. In addition, a metal layer94 is disposed so as to cover the conductive transparent electrode 92and the dielectric film 93. However, in such semiconductor laser devices90, an increase in the operating voltage is observed, and devicefailures probably caused by the operating voltage often occur, which hasbeen problematic.

It is desirable to provide a highly reliable nitride semiconductor laserdevice that includes, as an electrode material, conductive oxide, andenables improvements in electrical characteristics such as operatingvoltage, and a semiconductor laser apparatus including the nitridesemiconductor laser device.

SUMMARY

(1) According to an aspect of the disclosure, there is provided anitride semiconductor laser device including a substrate; afirst-conductivity-type semiconductor layer formed on the substrate; alight-emitting layer disposed on the first-conductivity-typesemiconductor layer; a second-conductivity-type semiconductor layerdisposed on the light-emitting layer; a strip ridge part disposed in thesecond-conductivity-type semiconductor layer; a conductive oxide layerdisposed so as to cover an upper surface of the ridge part and portionsof opposite side surfaces of the ridge part; a dielectric layer disposedso as to cover a portion of the conductive oxide layer; and a firstmetal layer disposed so as to cover the conductive oxide layer and thedielectric layer, wherein a portion of the conductive oxide layerdisposed on the upper surface of the ridge part has an exposed portionexposed through the dielectric layer, and the exposed portion is coveredwith the first metal layer.

(2) According to an aspect of the disclosure, there is provided asemiconductor laser apparatus including the nitride semiconductor laserdevice; and a package sealing the nitride semiconductor laser device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating a nitridesemiconductor laser device according to Embodiment 1 of the presentdisclosure;

FIG. 2 is a schematic sectional view illustrating another example of thenitride semiconductor laser device according to Embodiment 1 of thepresent disclosure;

FIG. 3 is a schematic sectional view illustrating a nitridesemiconductor laser device according to Embodiment 2 of the presentdisclosure;

FIG. 4 is a schematic sectional view for explaining the nitridesemiconductor laser device of FIG. 3;

FIG. 5 is a schematic sectional view for further explaining the nitridesemiconductor laser device of FIG. 3;

FIG. 6 is a schematic sectional view illustrating a nitridesemiconductor laser device according to Embodiment 3 of the presentdisclosure;

FIG. 7 is a schematic sectional view illustrating a nitridesemiconductor laser device according to another embodiment of thepresent disclosure;

FIG. 8 is an explanatory view illustrating electrical characteristics ofthe nitride semiconductor laser device;

FIG. 9 is a graph illustrating results of evaluation of leakage currentin the nitride semiconductor laser device and withstand voltage for theleakage current;

FIG. 10 is a schematic sectional view of a wafer of a nitridesemiconductor laser device according to an Example of the presentdisclosure; and

FIG. 11 is a partial sectional view illustrating a semiconductor laserdevice of an existing example.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, nitride semiconductor laser devices and a semiconductorlaser apparatus according to embodiments of the present disclosure willbe described with reference to drawings. Incidentally, in the drawingsdescribed below, in order to clarify and simplify the drawings,dimensions such as length, width, and thickness do not reflect actualrelations therebetween. In particular, the drawings are drawn withrelatively appropriately increased thicknesses. The same reference signsin drawings denote the same portions or corresponding portions.

Embodiment 1

FIG. 1 is a schematic sectional view illustrating a nitridesemiconductor laser device 10 according to Embodiment 1 of the presentdisclosure. As illustrated in the drawing, the nitride semiconductorlaser device 10 includes a substrate 11, a first-conductivity-typesemiconductor layer 12 formed on the substrate 11, a light-emittinglayer 13 disposed on the first-conductivity-type semiconductor layer 12,a second-conductivity-type semiconductor layer 14 disposed on thelight-emitting layer 13, a ridge-shaped ridge part 15 disposed in thesecond-conductivity-type semiconductor layer 14, a conductive oxidelayer 16 covering a portion of the ridge part 15, a dielectric layer 17covering a portion of the conductive oxide layer 16, and a first metallayer 18 covering the conductive oxide layer 16 and the dielectric layer17. On the back surface of the substrate 11, a first electrode 19 isprovided.

Substrate

The substrate 11 may be a nitride semiconductor substrate that is a GaNsubstrate or an AlGaN substrate. When the AlGaN substrate is used as thesubstrate 11, it functions as cladding, to suppress leakage of light tothe substrate, which occurs in the case of using the GaN substrate. Inthe case of using the AlGaN substrate, the AlGaN substrate may have anAl content ratio of 7% or less. Regarding the plane orientation of themain plane of the substrate 11, for example, a plane such as a polarplane (0001), a nonpolar plane (1-100), or a semi-polar plane (11-22)may be employed.

First-Conductivity-Type Semiconductor Layer

The first-conductivity-type semiconductor layer 12 may be an AlGaN layermainly doped with, as the first-conductivity-type impurity, Si, aSi-doped GaN layer, a Si-doped AlInGaN layer, or a Si-doped InGaN layer.Si used for doping the nitride semiconductor functions as an n-type inthe nitride semiconductor. The first-conductivity-type semiconductorlayer 12 may be constituted by a single layer, or may be constituted bya plurality of layers among the above-described layers.

Light-Emitting Layer

The light-emitting layer 13 is constituted by two or more well layersand one or more barrier layers. More specifically, the light-emittinglayer 13 may have well layer/barrier layer/well layer, or may have welllayer/barrier layer/well layer/barrier layer/well layer; in each ofthese cases, well layers are formed as outer layers of thelight-emitting layer 13.

In the light-emitting layer 13, such a well layer may be an InGaN layer;and such a barrier layer may be a GaN layer, an InGaN layer, or an AlGaNlayer. In the case of employing, as the barrier layer, an InGaN layer,it may be formed so as to have a lower In content ratio than an InGaNlayer serving as the well layer. In the case of employing, as thebarrier layer, an AlGaN layer, the Al content ratio may be set to 2% ormore and 8% or less.

The well layer has a layer thickness of 2.5 nm or more and 7.2 nm orless, preferably 3 nm or more and 4.5 nm or less. In the case of forminga well layer having a lasing wavelength of 450 nm or more, the welllayer needs to be formed so as to have a high In content ratio; whensuch a well layer having a high In content ratio has a layer thicknessof more than 5 nm, lattice distortion may cause crystal defects. Whenthe well layer has a layer thickness of less than 2.5 nm, gain maydecrease and threshold current density may increase, which isdisadvantageous. The barrier layer may have a layer thickness of 2.8 nmor more and 6 nm or less.

In the case of forming four or more well layers having a lasingwavelength of 450 nm or more, lattice distortion may cause seriouscrystal defects, resulting in degradation of laser characteristics. Forthis reason, the light-emitting layer 13 may have 2 or more and 3 orless well layers.

Second-Conductivity-Type Semiconductor Layer

The second-conductivity-type semiconductor layer 14 may be an AlGaNlayer doped with Mg as an impurity, a Mg-doped GaN layer, a Mg-dopedAlInGaN layer, or a Mg-doped InGaN layer. Mg used for doping the nitridesemiconductor functions as a p-type in the nitride semiconductor. Thesecond-conductivity-type semiconductor layer 14 may be constituted by asingle layer, or may be constituted by a plurality of layers among theabove-described layers.

For example, when the second-conductivity-type semiconductor layer 14 isconstituted by three layers, on the light-emitting layer 13, a firstp-type semiconductor layer, a second p-type semiconductor layer, and athird p-type semiconductor layer may be formed in this order to form thesecond-conductivity-type semiconductor layer 14.

The first p-type semiconductor layer may be formed as a Mg-containingAl_(x)Ga_(1−x)N (0≤x≤0.35) layer that has a layer thickness of 15 nm orless and functions as a blocking layer for electron carriers.

The second p-type semiconductor layer may be formed as a Mg-containingAl_(x)Ga_(1−x)N (0≤x≤0.055) layer that functions as a cladding layer.The layer thickness of the second p-type semiconductor layer is notparticularly limited, but is desirably 350 nm or less. A decrease in thelayer thickness of the second p-type semiconductor layer achieves adecrease in the operating voltage. For this reason, the layer thicknessis more preferably 280 nm or less.

The third p-type semiconductor layer may be formed as a Mg-containingIn_(x)Al_(y)Ga_(1−x−y)N (0≤x≤0.015, 0≤y≤0.1) layer that functions as acontact layer in contact with the conductive oxide layer 16. The layerthickness of the third p-type semiconductor layer is not particularlylimited, but is desirably 20 nm or less. A decrease in the layerthickness of the third p-type semiconductor layer achieves a decrease inthe operating voltage. For this reason, the layer thickness is morepreferably 10 nm or less.

The second-conductivity-type semiconductor layer 14 partially includesthe ridge part 15 formed so as to have a ridge shape. The ridge part 15is formed so as to have a strip shape (elongated shape) extending in adirection (the Y direction in FIG. 1) orthogonal to the edge surfaces ofthe nitride semiconductor laser device 10.

Conductive Oxide Layer

On the ridge part 15, the conductive oxide layer 16 is formed. In theconfiguration illustrated in FIG. 1, the conductive oxide layer 16 isformed with a strip shape so as to cover the whole upper surface (topsurface) of the ridge part 15, and to cover partially surfaces (oppositeto each other in the X direction) of the ridge part 15.

Incidentally, in the following description, a surface positioned at thetop portion of the ridge part 15 is referred to as an upper surface 151of the ridge part 15; when the X direction in FIG. 1 is defined as theleft-right direction, the left-right opposite surfaces of the ridge part15 (inclined surfaces opposite to each other in the X direction) arereferred to as side surfaces 152 of the ridge part 15; and the uppersurfaces of the second-conductivity-type semiconductor layer 14positioned on lower-end opposite sides of the ridge part 15 (left-rightopposite sides of the ridge part 15) are referred to as bottom surfaces153 of the ridge part 15.

Half or more (from the upper surface 151) of the region of each sidesurface 152 of the ridge part 15 may be covered with the conductiveoxide layer 16. For example, when the second-conductivity-typesemiconductor layer 14 is constituted by three layers that are the firstp-type semiconductor layer, the second p-type semiconductor layer, andthe third p-type semiconductor layer, the conductive oxide layer 16formed on the upper surface of the ridge part 15 is disposed in contactwith the third p-type semiconductor layer. The conductive oxide layer 16formed on the opposite side surfaces of the ridge part 15 may bedisposed in contact with the side surfaces 152 of the ridge part 15 inthe third p-type semiconductor layer and the side surfaces 152 of theridge part 15 in the second p-type semiconductor layer.

This configuration achieves an increase in the coverage ratio ofcovering the side surfaces 152 of the ridge part 15 with the conductiveoxide layer 16. Such an increase in the coverage ratio of the ridge part15 covered with the conductive oxide layer 16 effectively preventshydrogen generated from the dielectric layer 17 from permeating into thesecond-conductivity-type semiconductor layer 14.

Incidentally, the second-conductivity-type semiconductor layer 14 mayfurther include a plurality of layers between the second p-typesemiconductor layer and the third p-type semiconductor layer. When theconductive oxide layer 16 is formed so as to extend to the bottomsurfaces 153 on the opposite sides of the ridge part 15 (refer toEmbodiment 2 described later), the conductive oxide layer 16 may bedisposed in contact with the second p-type semiconductor layer exposedduring formation of the ridge part 15.

The conductive oxide layer 16 may be formed of, for example, indium tinoxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or gallium oxide(GaO₃). The conductive oxide layer 16 may be formed with a layerthickness of 50 nm or more and 500 nm or less.

Dielectric Layer

The conductive oxide layer 16 is partially covered with the dielectriclayer 17 that confines current. The dielectric layer 17 ensuresinsulation between the upper surfaces of the second-conductivity-typesemiconductor layer 14, which are the bottom surface regions of theridge part 15, and the side surfaces 152 of the ridge part 15, and alsoensures a refractive index difference relative to thesecond-conductivity-type semiconductor layer 14.

In the configuration illustrated in FIG. 1, the dielectric layer 17 isformed on the second-conductivity-type semiconductor layer 14 so as tocover left and right opposite side surfaces 152 of the ridge part 15 andportions of the upper surface 151 of toe ridge part 15.

Thus, the opposite side surfaces 152 of the ridge part 15 are coveredwith the conductive oxide layer 16 and the dielectric layer 17. Thedielectric layer 17 is disposed also on sides (opposite to each other inthe X direction) of the ridge part 15. The portion of the conductiveoxide layer 16 covering the upper surface 151 of the ridge part 15 (theportion being positioned at the upper surface 151 of the ridge part 15)includes portions covered with the dielectric layer 17 and an exposedportion 154 exposed through the dielectric layer 17.

In the upper surface 151 of the ridge part 15, edge portions opposite toeach other in the X direction are covered with the dielectric layer 17,and the exposed portion 154 in the central portion is exposed throughthe dielectric layer 17. The exposed portion 154 is formed with a widthnarrower than the width (in the X direction) of the upper surface 151 ofthe ridge part 15, and is disposed so as to extend in the Y direction.

The dielectric layer 17 may be formed of, for example, silicon oxide,aluminum oxide (Al₂O₃), titanium oxide (TiO₂), tantalum oxide (Ta₂O₅),or zirconium oxide (ZrO₂). The dielectric layer 17 may be formed with alayer thickness of 100 nm or more and 500 nm or less.

First Metal Layer

The exposed portion 154 of the conductive oxide layer 16 is covered withthe first metal layer 18. The first metal layer 18 is formed so as tocover the exposed portion 154 of the conductive oxide layer 16 exposedthrough the dielectric layer 17, and the dielectric layer 17.

The first metal layer 18 may be formed of, for example, titanium,nickel, gold, palladium, platinum, molybdenum, or aluminum. The firstmetal layer 18 is not limited to a single layer, and may be constitutedby a plurality of metal layers.

The inventors of the present disclosure performed studies and, as aresult, have found the following findings: the above-described increasein the operating voltage of the semiconductor laser device particularlyoccurs in a nitride semiconductor laser device having a ridge-strip-typecurrent confinement structure containing conductive oxide where adielectric layer for blocking current is disposed in contact with allthe side surfaces of the ridge part of the second-conductivity-typesemiconductor layer, so that the semiconductor laser device cannotsufficiently exert its performance.

This is inferentially caused in the following manner: a heat treatmentperformed after formation of the dielectric film in order to lower thecontact resistance between layers that are the second-conductivity-typesemiconductor layer, the conductive oxide layer, and the first metallayer, turns hydrogen or water adsorbed on the dielectric layer, intodesorbed or decomposed hydrogen; the hydrogen permeates into thesecond-conductivity-type semiconductor layer, to bond to Mg contained inthe second-conductivity-type nitride semiconductor layer, to deactivateMg.

In general, as the dopant for the second-conductivity-type semiconductorlayer, Mg is used; however, when a hydrogen atom bonds to Mg, changeinto the p-type is known to be inhibited, which results in an increasein the operating voltage.

In the nitride semiconductor laser device 10 according to thisembodiment, a region into which current is substantially injected.(current confinement region) is the ridge part 15 of thesecond-conductivity-type semiconductor layer 14. Thus, hydrogengenerated from the dielectric layer 17 is prevented from permeating intothe ridge part 15 of the second-conductivity-type semiconductor layer14, to thereby suppress the increase in the voltage due to currentinjection failure.

In the nitride semiconductor laser device 10 according to thisembodiment, the conductive oxide layer 16, which is a film impermeableto hydrogen atoms, is formed so as to cover at least the upper surface151 and portions of the side surfaces 152 of the ridge part 15 of thesecond-conductivity-type semiconductor layer 14. This prevents hydrogengenerated from the dielectric layer 17 from permeating into a regionnear the upper surface 151 of the ridge part 15 of thesecond-conductivity-type semiconductor layer 14. This prevents thedeterioration in the operating voltage in the nitride semiconductorlaser device 10, to thereby improve the electrical characteristics.

As described above, the conductive oxide layer 16 may be disposed so asto cover half or more of the side surfaces 152 of the ridge part 15.This achieves an increased coverage ratio of the conductive oxide layer16 covering the side surfaces 152 of the ridge part 15, to suppresspermeation of hydrogen generated from the dielectric layer 17 into thesecond-conductivity-type semiconductor layer 14.

FIG. 2 is a schematic sectional view illustrating another example of thenitride semiconductor laser device 10 according to Embodiment 1 of thepresent disclosure. As illustrated in the drawing, in the nitridesemiconductor laser device 10, the conductive oxide layer 16 may beformed so as to cover the upper surface 151 of the ridge part 15 and allthe opposite side surfaces 152 of the ridge part 15.

In this case, the side surfaces 152 of the ridge part 15 are completelycovered with the conductive oxide layer 16. This further suppressespermeation of hydrogen generated from the dielectric layer 17 into thesecond-conductivity-type semiconductor layer 14.

Embodiment 2

FIG. 3 to FIG. 5 are schematic sectional views illustrating a nitridesemiconductor laser device 20 according to Embodiment 2 of the presentdisclosure. The nitride semiconductor laser device 20 according toEmbodiment 2 is characterized by the form of the conductive oxide layer16, but the other basic elements are the same as in the nitridesemiconductor laser device 10 described in Embodiment 1. For thisreason, the conductive oxide layer 16 different from Embodiment 1 willbe described in detail, but the other elements will be denoted by thesame reference signs as in Embodiment 1 and will not be described.

As illustrated in FIG. 3, in the nitride semiconductor laser device 20,the conductive oxide layer 16 is disposed so as to cover the uppersurface 151 of the ridge part 15, the opposite side surfaces 152 of theridge part 15, and portions of the bottom surfaces 153 of the ridge part15 (the upper surfaces of the second-conductivity-type semiconductorlayer 14). The conductive oxide layer 16 is continuously disposed fromthe upper surface 151 to the bottom surfaces 153 of the ridge part 15.

In general, the ridge-type semiconductor laser device is designed suchthat current is injected from the upper surface of the ridge part, andlight is concentrated in the active layer immediately below theprotruding ridge shape. This is because this design enables efficientcombination of current and light, which results in improvements in thelaser characteristics. Thus, current flowing out into regions other thanthe light concentration region causes loss, which results in a decreasein the power efficiency.

By contrast, in the nitride semiconductor laser device 20 according tothis embodiment illustrated in FIG. 3, the conductive oxide layer 16 isformed on the side surfaces 152 of the ridge part 15 and the bottomsurfaces 153 of the ridge part 15; in general, current flowing throughthe conductive oxide layer 16 tends to flow in the vertical direction(that is the upright direction in the drawing and is the layer stackingdirection perpendicular to the main surface of the substrate 11)relative to the horizontal direction (lateral direction), so that a lowproportion of current leaks into regions (the conductive oxide layer 16extending over the bottom surfaces 153 on opposite sides of the ridgepart 15) other than the light concentration region. Rather, theconfiguration in which the side surfaces 152 of the ridge part 15 arecompletely covered with the conductive oxide layer 16 almost preventshydrogen generated from the dielectric layer 17 from permeating into thesecond-conductivity-type semiconductor layer 14. This prevents, in thenitride semiconductor laser device 20, the deterioration in theoperating voltage, to thereby further improve the electricalcharacteristics.

For example, as illustrated in FIG. 3, the conductive oxide layer 16 isdisposed so as to cover portions of the bottom surfaces 153 on oppositesides of the ridge part 15; the conductive oxide layer 16 may have awidth W1 of 1.5 μm or less. This reduces the effect of leakage currenton the conductive oxide layer 16 extending over the bottom surfaces 153on opposite sides of the ridge part 15, to thereby prevent the decreasein the power efficiency.

The conductive oxide layer 16 has a refractive index higher than therefractive index of the dielectric layer 17. As illustrated in FIG. 4,the conductive oxide layer 16 extending over the bottom surfaces 153 onopposite sides of the ridge part 15 may have a width W1 that is ⅕ orless of a width (strip width) W2 of the upper surface 151 of the ridgepart 15.

The conductive oxide layer 16 formed of, for example, ITO and thedielectric layer 17 formed of, for example, SiO₂ have lower refractiveindexes than the second-conductivity-type semiconductor layer 14. Thus,the refractive indexes of the conductive oxide layer 16, the dielectriclayer 17, and the second-conductivity-type semiconductor layer 14satisfy the following relation:

-   -   Second-conductivity-type semiconductor layer 14>Conductive oxide        layer 16>Dielectric layer 17

The distance d1 between the conductive oxide layer 16 formed on thebottom surfaces 153 on opposite sides of the ridge part 15, and thelight-emitting layer 13 positioned under the dielectric layer 17 isshorter than the distance d2 between the conductive oxide layer 16formed on the upper surface 151 of the ridge part 15, and thelight-emitting layer 13 positioned under the dielectric layer 17.

The nitride semiconductor laser device 20 has the above-describedconfiguration, so that the refractive index within the light-emittinglayer 13 decreases in a direction perpendicular to the ridge part 15.Specifically, as illustrated in FIG. 4, in the light-emitting layer 13of the nitride semiconductor laser device 20, when a light-emittinglayer region immediately below the ridge part 15 is defined as N1, alight-emitting layer region immediately below the conductive oxide layer16 extending over the bottom surfaces 153 on opposite sides of the ridgepart 15 is defined as N2, and a light-emitting layer region immediatelybelow the dielectric layer 17 formed on the bottom surfaces 153 onopposite sides of the ridge part 15 is defined as N3, the refractiveindexes of the light-emitting layer regions N1, N2, and N3 satisfy thefollowing relation:

-   -   Light-emitting layer region N1>Light-emitting layer region        N2>Light-emitting layer region N3.

Thus, in the nitride semiconductor laser device 20 according to thisembodiment, the laser beam propagating within the light-emitting layer13 concentrates in high refractive index regions, so that thelight-emitting layer region N1 and the two light-emitting layer regionsN2 contribute, to thereby achieve an increase in the width of the laserbeam propagating within the light-emitting layer 13. This increase issignificant, compared with existing ridge-type semiconductor laserdevices not including the conductive oxide layer on the bottom surfacesof the ridge part.

In addition, in existing ridge-type semiconductor lasers, in order toincrease the width of the laser beam propagating through thelight-emitting layer or to prevent optical damage (Catastrophic OpticalDamage: COD), the width (W2) of the upper surface of the ridge partneeds to be increased. This causes an increase in the operating current,to cause an increase in the power consumption, which has beenproblematic.

By contrast, in the nitride semiconductor laser device 20 according tothis embodiment, without changing the width W2 of the upper surface ofthe ridge part 15, the width of the laser beam emitted from thelight-emitting layer 13 can be changed on the basis of the width W1 ofthe conductive oxide layer 16. The width W1 of the conductive oxidelayer 16 may be ⅕ or less of the width W2 of the upper surface of theridge part 15; when the width W1 is larger than this range, thethreshold current increases.

As illustrated in FIG. 5, in the conductive oxide layer 16 of thenitride semiconductor laser device 20, when the layer thickness of theconductive oxide layer 16 formed on the upper surface 151 of the ridgepart 15 is defined as T1, the layer thickness of the conductive oxidelayer 16 formed on the side surfaces 152 of the ridge part 15 is definedas T2, and the layer thickness of the conductive oxide layer 16 formedover the bottom surfaces 153 on opposite sides of the ridge part 15 isdefined as T3, these layer thicknesses T1, T2, and T3 satisfy thefollowing relation:

-   -   T1>T2 or T1>T3.

This causes an increase in the electric resistance against currentflowing (in the horizontal direction) in the conductive oxide layer 16,to thereby further suppress leakage of current to the conductive oxidelayer 16 extending over the bottom surfaces 153 on opposite sides of theridge part 15.

The conductive oxide layer 16 on the upper surface 151 of the ridge part15 is formed so as to have a layer thickness T1 larger than the otherlayer thicknesses (T2 and T3), for example, in the following manner: forexample, a sputtering apparatus is used to form the conductive oxidelayer 16 on the upper surface, the side surfaces, and the bottomsurfaces of the ridge part 15, and subsequently a photoresist techniqueis used to form again the conductive oxide layer 16 only on the uppersurface of the ridge part 15.

Also in the nitride semiconductor laser device 20 according toEmbodiment 2, the conductive oxide layer 16, which is a film impermeableto hydrogen atoms, is disposed so as to cover the upper surface 151, theside surfaces 152, and portions of the bottom surfaces 153 of the ridgepart 15, to thereby prevent hydrogen generated from the dielectric layer17 from permeating into a region near the upper surface 151 of the ridgepart 15 of the second-conductivity-type semiconductor layer 14. Inaddition, leakage of current to the conductive oxide layer 16 extendingover the bottom surfaces 153 on opposite sides of the ridge part 15 canbe further suppressed. Thus, the deterioration in the operating voltagein the nitride semiconductor laser device 20 is prevented, to improvethe electrical characteristics.

Embodiment 3

FIG. 6 is a schematic sectional view illustrating a nitridesemiconductor laser device 30 according to Embodiment 3. The nitridesemiconductor laser device 30 according to Embodiment 3 is characterizedin that a second metal layer 31 is disposed between thesecond-conductivity-type semiconductor layer 14 and the conductive oxidelayer 16, but the other basic elements are the same as in the nitridesemiconductor laser device described in Embodiment 1 or 2. For thisreason, the second metal layer 31 will be described in detail, but theother elements will be denoted by the same reference signs as inEmbodiment 1 or 2 and will not be described.

As illustrated in FIG. 6, in the nitride semiconductor laser device 30,the second metal layer 31 is disposed in contact with and between thesecond-conductivity-type semiconductor layer 14 and the conductive oxidelayer 16.

The second metal layer 31 is characterized by being a film impermeableto hydrogen. Thus, the second metal layer 31 disposed between thesecond-conductivity-type semiconductor layer 14 and the conductive oxidelayer 16 enables further prevention of entry of hydrogen atoms into thesecond-conductivity-type semiconductor layer 14.

The second metal layer 31 may be formed of a hydrogen-absorbing alloyof, for example, palladium, nickel, or titanium. When the second metallayer 31 is formed of such a hydrogen-absorbing alloy, in addition tohydrogen generated from the dielectric layer 17, hydrogen atomsunintentionally introduced during the process of producing thesecond-conductivity-type semiconductor layer 14 can be extracted byabsorption.

In general, in the nitride semiconductor laser device, thesecond-conductivity-type semiconductor layer has high electricresistance; in order to decrease the operating voltage, thesecond-conductivity-type semiconductor layer may be formed with asmaller Paver thickness. However, when the distance D between the bottomsurface of the second metal layer 31 and the upper surface of thelight-emitting layer 13 is 400 nm or less, the laser beam is partiallyabsorbed by the second metal layer 31, which results in deterioration inthe power-light conversion efficiency. For this reason, in the nitridesemiconductor laser device 30 according to this embodiment, the secondmetal layer 31 preferably has a layer thickness of 1.5 nm or less, morepreferably 1 nm or less. This enables, without causing deterioration inthe operating voltage or deterioration in the power-light conversionefficiency, improvements in the electrical characteristics.

Embodiment 4

FIG. 7 and FIG. 8 are schematic sectional views of a nitridesemiconductor laser device 30 according to Embodiment 4. The nitridesemiconductor laser devices 10, 20, and 30 accord to the presentdisclosure can be practiced in, in addition to the above-describedconfigurations described in Embodiments, other various forms. Thus, theabove-described Embodiments according to the present disclosure are mereexamples of the present disclosure, and do not limit the presentdisclosure.

For example, the first metal layer 18 disposed so as to cover theconductive oxide layer 16 and the dielectric layer 17 is not limited tothe single layer configuration described above in Embodiments, and mayhave a configuration including a plurality of layers. As illustrated inFIG. 7, in the nitride semiconductor laser device 30, the first metallayer 18 may be constituted by a plurality of metal layers. The firstmetal layer 18 may have a configuration in which, for example, atitanium (Ti) layer 181 and a gold (Au) layer 182 are stacked.

The conductive oxide layer 16 is disposed so as to cover the uppersurface 151 of the ridge part 15 and the opposite side surfaces 152 ofthe ridge part 15, and so as to protrude over at least one of the bottomsurfaces 153 on the lower-end opposite sides of the ridge part 15 tocover a portion of the upper surface of the second-conductivity-typesemiconductor layer 14. This provides a configuration in which theconductive oxide layer 16 and the second-conductivity-type semiconductorlayer 14 are in contact with each other.

In this case, as illustrated in FIG. 8, when forward voltage is applied,forward current mainly flows from the conductive oxide layer 16 to theridge part 15 (second-conductivity-type semiconductor layer 14). This isbecause the conductive oxide layer 16 has high electric resistance inthe horizontal direction (lateral direction), so that current flowingthrough the conductive oxide layer 16 on the upper surface 151 of theridge part 15 tends to flow in the vertical direction (uprightdirection) relative to the horizontal direction. Specifically, currenttends not to flow from the conductive oxide layer 16 on the uppersurface 151 of the ridge part 15 to the side surfaces 152 and the bottomsurfaces 153 of the ridge part 15.

On the other hand, when reverse voltage is applied, the depletion layerexpands, before it reaches the conductive oxide layer 16 on the uppersurface 151 of the ridge part 15, to the conductive oxide layer 16 onthe bottom surfaces 153 of the ridge part 15, and leakage occurs alongsmall arrows in FIG. 8 (punch-through). As a result, device breakdowncan be suppressed.

In order to provide such characteristics, the second-conductivity-typesemiconductor layer 14 may have a Mg concentration of, for example,5×10¹⁶ cm⁻³ or more and 1×10¹⁹ cm⁻³ or less. On the bottom surfaces 153of the ridge part 15, the second-conductivity-type semiconductor layer14 may have a thickness t of, for example, 10 nm or more and 300 nm orless.

FIG. 9 is a graph illustrating result of evaluation of leakage currentoccurring upon application of a reverse voltage of 15 V, and withstandvoltage (withstanding voltage) of the laser device during occurrence ofthe leakage current. The withstand voltage is the voltage limit underwhich the nitride semiconductor laser device does not malfunction or isnot broken down. On the basis of this, the nitride semiconductor laserdevice 30 according to this Embodiment was evaluated for electro staticdischarge (ESD) resistance. As a result, the withstand voltage was foundto be high, compared with semiconductor laser devices having an existingconfiguration in which a conductive electrode is disposed only on theupper surface of the ridge part (refer to FIG. 11). It has also beenfound out that, in the nitride semiconductor laser devices 30 accordingto this Embodiment, most of devices having high ESD resistance cause,upon application of a reverse voltage of 15 V, occurrence of a leakagecurrent of 10 μA or more. This fact agrees with the above-describedmechanism of suppressing device breakdown at the reverse withstandvoltage. In general, the ESD test is a destructive inspection and hencecannot be used to test all the products. By contrast, when devicesaccording to the present disclosure under application of a reversevoltage of 15 V are found to cause occurrence of a leakage current of 10μA or more, these devices can be selected as having ESD resistance.

Furthermore, in the nitride semiconductor laser device 30 according tothis Embodiment, the conductive oxide layer 16 is continuously disposedso as to cover the upper surface 151 of the ridge part 15, the oppositeside surfaces 152 of the ridge part 15, and the bottom surface 153 ofthe ridge part 15; thus, the nitride semiconductor laser device 30 hashigh ESD resistance, and causes occurrence of weak current leakage uponapplication of reverse voltage. Thus, the nitride semiconductor laserdevice 30 enables suppression of device breakdown upon application ofreverse voltage, and uses the conductive oxide layer 16 as a deviceprotective circuit.

A semiconductor laser apparatus according to the present disclosure mayinclude the nitride semiconductor laser device 10, 20, or 30 describedin the above-described Embodiments, a submount having a mount surface onwhich the nitride semiconductor laser device is mounted, and a package100 hermetically sealing the nitride semiconductor laser device 10, 20,or 30 and the submount.

Existing semiconductor laser devices do not sufficiently resist the backelectromotive force and hence undergo device breakdown due to, forexample, static electricity, which has been problematic. For thisreason, in order to suppress device breakdown, such an existingsemiconductor laser device needs to be mounted, within a single package,together with a protective device such as a Zener diode. By contrast, asdescribed above, the nitride semiconductor laser device 30 according tothis Embodiment has a function of a device protective circuit, so thatthe necessity of using the protective device such as a Zener diode hasbeen eliminated, and a semiconductor laser apparatus including thenitride semiconductor laser device 30 does not need such a protectivedevice mounted within the same package.

As has been described so far, the nitride semiconductor laser devices10, 20, and 30 according to the present disclosure achieve improvementsin the electrical characteristics relative to existing ones, to provideimproved reliability.

Example 1

FIG. 10 is a schematic sectional view of a wafer 110 in a nitridesemiconductor laser device according to an Example of the presentdisclosure.

The wafer 110 has a configuration in which, on the (0001) plane of ann-type GaN substrate 111, an n-type GaN layer 112, an n-type AlGaNcladding layer 113, an n-type GaN layer 114, a first non-doped InGaNoptical guide layer 115, a first non-doped GaN layer 116, alight-emitting layer 117, a second non-doped GaN layer 118, a secondnon-doped InGaN optical guide layer 119, a p-type AlGaN layer 120, ap-type AlGaN cladding layer 121, and a p-type GaN contact layer 122 aresequentially stacked.

The n-type GaN layer 112, the n-type AlGaN cladding layer 113, and then-type GaN layer 114 correspond to the first-conductivity-typesemiconductor layer 12. The p-type AlGaN layer 120, the p-type AlGaNcladding layer 121, and the p-type GaN contact layer 122 correspond tothe second-conductivity-type semiconductor layer 14.

In this Example, the nitride semiconductor laser device was produced inthe following manner.

Within an MOCVD apparatus, the n-type GaN substrate 111 is first heatedto 1050° C. Subsequently, while the n-type GaN substrate 111 is held atthe temperature, a group III element source trimethylagallium (TMG),ammonia gas, and a doping gas SiH₄ are introduced, to form, on then-type GaN substrate 111, the n-type GaN layer 112 having a thickness of0.5 μm.

The n-type GaN layer 112 is formed in order to improve the surfacemorphology of the polished n-type GaN substrate 111, and is formed inorder to relax the residual stress strain in the surface of the n-typeGaN substrate 111, to obtain the surface of the n-type GaN substrate 111suitable for epitaxial growth.

Subsequently, into the MOCVD apparatus, a group III element sourcetrimethylaluminum (TMA) is further added, to form the n-type AlGaNcladding layer 113 having a thickness of 1.2 μm and a Si impurityconcentration of 1×10¹⁸ atoms/cm³. The n-type AlGaN cladding layer 113was formed with an Al content ratio of 7%.

Subsequently, the introduction of TMA into the MOCVD apparatus isstopped, to form the n-type GaN layer 114 having a thickness of 0.2 μm.The n-type GaN layer 114 was formed with a Si impurity concentration of1×10¹⁸ atoms/cm³.

Subsequently, the temperature of the n-type GaN substrate 111 is loweredto 800° C. Into the MOCVD apparatus, trimethylindium (TMI) is added andthe introduction of SiH₄ is stopped, to form the first undopedIn_(0.04)Ga_(0.96)N optical guide layer 115 having a thickness of 100nm.

On the first, undoped In_(0.04)Ga_(0.96)N optical guide layer 115, thefirst GaN layer 116 having a thickness of 3 nm is formed. Subsequently,on the first GaN layer 116, an undoped In_(0.16)Ga_(0.84)N well layerhaving a thickness of 3 nm, an undoped GaN barrier layer having athickness of 5 nm, and an undoped In_(0.16)Ga_(0.84)N well layer havinga thickness of 3 nm are sequentially stacked to form the light-emittinglayer 117. Furthermore, on the light-emitting layer 117, the second GaNlayer 118 having a thickness of 3 nm and the second non-dopedIn_(0.04)Ga_(0.96)N optical guide layer 119 having a thickness of 100 nmare sequentially formed.

Subsequently, the temperature of the n-type GaN substrate 111 is againraised to 1050° C., and Cp₂Mg source gas) is fed, to form sequentiallythe p-type Al_(0.20)Ga_(0.80)N layer 120 having a thickness of 10 nm andhaving a Mg concentration of 4×10¹⁸ cm⁻³, the p-type Al_(0.04)Ga_(0.96)Ncladding layer 121 having a thickness of 0.3 μm and having a Mgconcentration of 3×10¹⁸ cm⁻⁸, and the p-type GaN contact layer 122having a thickness of 10 nm and having a Mg concentration of 1×10¹⁹cm⁻³. This provides the wafer 110.

Incidentally, in the case of using, as the conductive oxide layer 16,indium tin oxide (ITO), the p-type GaN contact layer 122 may be replacedby a p-type InGaN contact layer. This is because InGaN provides a lowercontact resistance than GaN.

Subsequently, a mask layer having a predetermined pattern is formed onthe wafer 110, and a strip ridge part is formed. On the surface of thep-type GaN contact layer 122, a CVD apparatus is used to form, as thefirst mask layer, a SiO₂ film with a film thickness of 300 nm.Subsequently, photoresist is applied, and an RIE (reactive ion etching)apparatus is used to form, in the first mask layer, a strip patternhaving a width of 15 μm.

Subsequently, the surface of the p-type GaN contact layer 122 exposedthrough the opening of the first mask layer is etched with the RIEapparatus until a portion of the p-type Al_(0.04)Ga_(0.96)N claddinglayer 121 is exposed. The first mask layer is removed by wet etching, toform a strip ridge part in which the upper surface of the ridge part hasa width of 15 μm and the height between the upper surface of the ridgepart and the bottom surface of the ridge is 190 nm.

Subsequently, a sputtering apparatus is used to form a film of aconductive oxide ITO to 200 nm so as to cover the ridge part. Anordinary photolithography technique is used to form a photoresist maskprotruding, by about 1 μm, from opposite sides of the ridge part, andhaving a width of 17 μm. Subsequently, ITO exposed through the openingof the photoresist mask is etched by wet etching, to form ITO disposedon the upper surface and opposite side surfaces of the ridge part andprotruding, by 1 μm, over the bottom surfaces on opposite sides of theridge part. Subsequently, the photoresist mask is removed.

When the second metal layer formed of palladium is disposed between thep-type GaN contact layer 122 and ITO on the upper surface of the ridgepart, it may be formed, prior to formation of the ITO film, on the uppersurface of the ridge part by using a photolithography technique and avapor deposition apparatus.

Subsequently, a CVD apparatus is used to form a dielectric layer formedof SiO₂ to 200 nm so as to cover the ITO. Subsequently, aphotolithography technique is used to form an opening by etching aportion of SiO₂ formed on the upper surface of the ridge part.Subsequently, a metal vapor deposition apparatus is used to performvapor deposition of, as the first metal layer, titanium to 15 nm so asto cover the ITO exposed through the opening and the dielectric layerformed of SiO₂. After the first metal layer is formed, the wafer istemporarily taken out of the vapor deposition apparatus, and subjectedto heat treatment at a temperature of several hundred degrees Celsius.This heat treatment causes a decrease in the contact resistance betweenlayers of the second-conductivity-type semiconductor layer, theconductive oxide layer (for example, ITO), and the first metal layer,which contributes to a decrease in the voltage.

After the heat treatment, the metal vapor deposition apparatus is usedagain to achieve vapor deposition of gold to a thickness of 800 nm ontitanium forming the first metal layer.

Subsequently, the back surface of the n-type GaN substrate 111 wassubjected to grinding and polishing treatment such that the thickness isreduced to about 90 nm. On one back surface of the n-type GaN substrate111, as the first electrode, vapor deposition of titanium and gold isperformed respectively to 15 nm and 400 nm.

In addition, the ridge part is cleaved such that the long side of thestrip has a length of 1200 μm. On the opposite edge surfaces of theridge part provided by the cleaving, protective films are formed.Division into chips is performed such that the chip width is 200 μm. Inthis way, nitride semiconductor laser devices were obtained.

Example 2

This Example has the same features as those disclosed in Embodiments 1to 3 or Example 1 except that the layer thicknesses of the conductiveoxide layer 16 according to Embodiment 2 were set as follows: T1=200 nm,T2=80 nm, and T3=150 nm.

Example 3

This Example has the same features as those disclosed in Embodiments 1to 3 or Example 1 except that the layer thicknesses of the conductiveoxide layer 16 according to Embodiment 2 were set as follows: T1=250 nm,T2=105 nm, and T3=100 nm.

Example 4

This Example has the same features as those disclosed in Embodiments 1to 3 or Example 1 except that the layer thicknesses of the conductiveoxide layer 16 according to Embodiment 2 were set as follows: T1=150 nm,T2=60 nm, and T3=60 nm.

Example 5

This Example has the same features as those disclosed in Embodiments 1to 3 or Example 1 except that the width W1 of the conductive oxide layer16 and the width W2 of the upper surface of the ridge part 15 accordingto Embodiment 2 were respectively set to 3 μm and 35 μm.

Example 6

This Example has the same features as those disclosed in Embodiments 1to 3 or Example 1 except that the width W1 of the conductive oxide layer16 and the width W2 of the upper surface of the ridge part 15 accordingto Embodiment 2 were respectively set to 9 μm and 45 μm.

The nitride semiconductor laser devices according to Examples of thepresent disclosure produced above are operated at low voltage and have alow level of device defectiveness due to abnormal voltage, hence havehigh reliability, compared with existing semiconductor laser devicescontaining conductive oxide in which the dielectric layer is formed onall the side surfaces of the ridge part.

Incidentally, the present disclosure is not limited to theabove-described configurations. The configurations can be changed invarious ways within the scope indicated with Claims. Embodimentsobtained by appropriately combining technical means disclosed indifferent embodiments also fall into the technical scope of the presentdisclosure. Furthermore, technical means disclosed in Embodiments may becombined to form novel technical features.

The present disclosure contains subject matter related to that disclosedin U.S. Provisional Application No. 62/798,392 filed on Jan. 29, 2019,the entire contents of which are hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A nitride semiconductor laser device comprising:a substrate; a first-conductivity-type semiconductor layer formed on thesubstrate; a light-emitting layer disposed on thefirst-conductivity-type semiconductor layer; a second-conductivity-typesemiconductor layer disposed on the light-emitting layer; a strip ridgepart disposed in the second-conductivity-type semiconductor layer; aconductive oxide layer disposed so as to cover an upper surface of theridge part and portions of opposite side surfaces of the ridge part; adielectric layer disposed so as to cover a portion of the conductiveoxide layer laying on the upper surface of the ridge part, and a firstmetal layer disposed so as to cover the conductive oxide layer and thedielectric layer, wherein a portion of the conductive oxide layerdisposed on the upper surface of the ridge part has an exposed portionexposed through the dielectric layer, and the exposed portion is coveredwith the first metal layer, and wherein the conductive oxide layer isdisposed so as to cover the upper surface of the ridge part, theopposite side surfaces of the ridge part, and a portion of an uppersurface of the second-conductivity-type semiconductor layer disposed onat least one of lower-end opposite sides of the ridge part.
 2. A nitridesemiconductor laser device comprising: a substrate; afirst-conductivity-type semiconductor layer formed on the substrate; alight-emitting layer disposed on the first-conductivity-typesemiconductor layer; a second-conductivity-type semiconductor layerdisposed on the light-emitting layer; a strip ridge part disposed in thesecond-conductivity-type semiconductor layer; a conductive oxide layerdisposed so as to cover an upper surface of the ridge part and portionsof opposite side surfaces of the ridge part; a dielectric layer disposedso as to cover a portion of the conductive oxide layer laying on theupper surface of the ridge part, and a first metal layer disposed so asto cover the conductive oxide layer and the dielectric layer, wherein aportion of the conductive oxide layer disposed on the upper surface ofthe ridge part has an exposed portion exposed through the dielectriclayer, and the exposed portion is covered with the first metal layer,and wherein the conductive oxide layer is disposed so as to cover theupper surface of the ridge part, the opposite side surfaces of the ridgepart, and portions of upper surfaces of the second-conductivity-typesemiconductor layer positioned on lower-end opposite sides of the ridgepart.
 3. The nitride semiconductor laser device according to claim 2,wherein portions of the conductive oxide layer that are disposed so asto cover the portions of the upper surfaces of thesecond-conductivity-type semiconductor layer positioned on the lower-endopposite sides of the ridge part have a width of 1.5 μm or less.
 4. Thenitride semiconductor laser device according to claim 2, wherein theconductive oxide layer has a refractive index higher than a refractiveindex of the dielectric layer, and includes portions that are disposedso as to cover the portions of the upper surfaces of thesecond-conductivity-type semiconductor layer positioned on the lower-endopposite sides of the ridge part, and that have a width that is ⅕ orless of a width of the upper surface of the ridge part.
 5. The nitridesemiconductor laser device according to claim 2, wherein the conductiveoxide layer satisfies a relation of T1>T2 or T1>T3, where T1 representsa layer thickness of the portion disposed on the upper surface of theridge part, T2 represents a layer thickness of portions disposed on theside surfaces of the ridge part, and T3 represents a layer thickness ofportions disposed so as to cover the portions of the upper surfaces ofthe second-conductivity-type semiconductor layer positioned on thelower-end opposite sides of the ridge part.
 6. A nitride semiconductorlaser device comprising: a substrate; a first-conductivity-typesemiconductor layer formed on the substrate; a light-emitting layerdisposed on the first-conductivity-type semiconductor layer; asecond-conductivity-type semiconductor layer disposed on thelight-emitting layer; a strip ridge part disposed in thesecond-conductivity-type semiconductor layer; a conductive oxide layerdisposed so as to cover an upper surface of the ridge part and portionsof opposite side surfaces of the ridge part; a dielectric layer disposedso as to cover a portion of the conductive oxide layer; and a firstmetal layer disposed so as to cover the conductive oxide layer and thedielectric layer, wherein a portion of the conductive oxide layerdisposed on the upper surface of the ridge part has an exposed portionexposed through the dielectric layer, and the exposed portion is coveredwith the first metal layer, and wherein the nitride semiconductor laserdevice further comprises a second metal layer disposed between and incontact with the second-conductivity-type semiconductor layer and theconductive oxide layer.
 7. The nitride semiconductor laser deviceaccording to claim 6, wherein the second metal layer contains palladium,nickel, or titanium.
 8. The nitride semiconductor laser device accordingto claim 6, wherein the second metal layer has a layer thickness of 1 nmor less.
 9. A semiconductor laser apparatus comprising: a nitridesemiconductor laser device; and a package sealing the nitridesemiconductor laser device, the nitride semiconductor laser devicecomprising: a substrate; a first-conductivity-type semiconductor layerformed on the substrate; a light-emitting layer disposed on thefirst-conductivity-type semiconductor layer; a second-conductivity-typesemiconductor layer disposed on the light-emitting layer; a strip ridgepart disposed in the second-conductivity-type semiconductor layer; aconductive oxide layer disposed so as to cover an upper surface of theridge part and portions of opposite side surfaces of the ridge part; adielectric layer disposed so as to cover a portion of the conductiveoxide layer; and a first metal layer disposed so as to cover theconductive oxide layer and the dielectric layer, wherein a portion ofthe conductive oxide layer disposed on the upper surface of the ridgepart has an exposed portion exposed through the dielectric layer, andthe exposed portion is covered with the first metal layer, wherein, whena voltage of −15 V is applied to the nitride semiconductor laser device,a leakage current of 10 μA or more occurs.
 10. The semiconductor laserapparatus according to claim 9, wherein no protective devices aremounted within the package.